1. Field of the Invention
The present invention relates to a magnetic head which is caused to fly over a rotating recording medium and read/write data, and particularly relates to a magnetic head which can control the clearance between a head and a recording medium by changing the protruding distance of a medium facing surface by thermal expansion caused by power distribution to and heating of a heater.
2. Description of the Related Arts
Conventionally, the flying height of a magnetic head with respect to a recording surface of a magnetic disk has to be reduced in order to realize a high recording density of a magnetic disk apparatus; and, recently, flying heights of 10 nm order have been realized. However, there are problems that collision with minute protrusions on the magnetic disk surface readily occur when the flying height of the magnetic head is reduced, and variations in the clearance of heads are present in the range of common differences of mechanisms; therefore, when contact with the medium is taken into consideration, flying heights smaller than the common differences cannot be set. As methods which solve the problems, methods of JP05-020635, JP2005-071546 and JP2005-276284 in which a heater is built in a head and the clearance between the head and a recording surface of a magnetic disk is controlled by utilizing a protruding phenomenon of a head flying surface caused by thermal expansion accompanying power distribution to the heater have been proposed. In JP05-020635, a thin film resistive element which functions as a heater is formed in an insulating layer of a thin film magnetic head, and power is distributed to the thin film resistive element in accordance with needs so as to heat the element, thereby causing a magnetic pole distal end portion to thermally expand and protrude. In JP2005-071546,with respect to increase in an apparatus temperature and an element temperature due to recording/reproduction, the power applied to an electric conductive film provided in a head is changed so as to maintain a constant element temperature, thereby maintaining a constant clearance between the element and a recording medium. In JP2005-276284, a heating device for increasing flying height which causes a part of an air bearing surface of a head to expand and protrude by heating so as to increase the distance between a recording/reproducing element and a magnetic disk surface and a heating device for reducing flying height which causes another part of the head air bearing surface to expand and protrude by heating so as to reduce the distance between the recording/reproducing element and the magnetic disk surface are provided in the head, and the flying height is corrected such that reproduction can be performed without causing collision, for example, upon activation of the apparatus.
In such a conventional magnetic head in which a heater is built in, the heater efficiency has to be enhanced so that a long protruding distance of a head can be provided with a little heating value of the heater. However, in conventional heater-built-in magnetic heads, what kind of disposition of a heater coil enhances the heater efficiency has not been satisfactorily mentioned, and there have been problems that the heater efficiency is low in some magnetic heads, and sufficient protruding distances cannot be obtained unless the amount of heater power distribution is increased. Also, there has been a problem that, when the temperature is increased too much by the power distribution to the heater coil in order to increase the protruding distance of the head, influence of migration of the heater coil or the heat to a read element or a write element is increased, and durability and performance of the magnetic head is deteriorated.